1. Field of the Invention
The present invention relates to a system and method for evaluating the effectiveness of a person to perform a task based on his/her preceding or predicted sleep pattern. More particularly, the present invention relates to a system and method for evaluating task effectiveness based on preceding or predicted sleep pattern using calculations that take into account circadian oscillators, a sleep reservoir, sleep intensity, performance use, sleep debt, interruptions to sleep, sleep inertia, and the demands of the task to be performed.
2. Background of the Invention
Numerous studies have been conducted relating to the analysis of sleep, alertness, and performance. One study is by Jewett and Kronauer, entitled xe2x80x9cInteractive Mathematical Models of Subjective Alertness and Cognitive Throughput in Humans,xe2x80x9d J. Biological Rhythms, 1999; 14(6): pages 588-597. The Jewett and Kronauer model (JK model hereafter) uses arbitrary units and then scales the result from 1 to 0 to fit the actual data, scaled from maximum to minimum. Consequently, the JK model does not make an independent prediction of performance without knowing the range of the results.
The JK model makes no provision for predicting the detrimental effects of sleep fragmentation and multiple interruptions in sleep. The JK model uses an oscillator with a large number of arbitrary parameters (van der Pol oscillator) to predict the asymmetrical cycle of performance around the clock. The JK model cannot adjust the phase of the circadian rhythm to reflect shift-work or transmeridian travel without detailed information about ambient light levels. Furthermore, the JK model cannot predict variations in any relevant aspect of operator performance that is of interest to the user.
U.S. Pat. No. 5,433,223 to Moore-Ede et al. discloses a method for predicting alertness and bio-compatibility of a work schedule of an individual. All of the methods described in Moore-Ede et al. are designed to predict alertness, not performance.
As represented by the foregoing examples, prior studies and patents do not provide a system or method for evaluating the effectiveness of a person to perform a specific task based on his or her previous sleep pattern. In addition, the prior studies are not designed to predict changes in task effectiveness based upon the pattern of sleep and activity that take into account many complex factors that contribute to the sleep experience.
The forgoing and other deficiencies are addressed by the present invention, which is directed to a system and method for evaluating the effectiveness of a person to perform a task based on his/her previous or predicted sleep pattern. The system and method can be used to predict changes in task effectiveness at any time of day, based upon numerous patterns of sleep and activity (wakefulness), either experienced or planned for the future. The system and method take into account progressive increases in sleep deprivation (fatigue), the effects of the time of day (circadian rhythms) on performance, and changes in the time when a person sleeps and works (shift work and trans-meridian phase shifts).
The system and method for evaluating the effectiveness of a person to perform a task can be employed to schedule sleep and wake periods relative to specific tasks depending on the skills required for the task, such as helping to schedule drivers and pilots to avoid the problems caused by fatigue. Furthermore, the system can be used to anticipate the detrimental effects of jet lag, the beneficial effects of naps, the variations in performance and attention due to circadian rhythms, the variations in sleep quality with time of day and environmental conditions, the safest times to perform difficult tasks, and to help determine when to take sedatives or stimulants, if needed. The system and method may be used to retrospectively analyze the sleep history of a person making a performance error, such as driving a truck off the road, in order to determine if the error was, potentially, related to fatigue and/or circadian variations in performance.